Liquid crystal display devices include a TFT substrate having a pixel electrode, a thin-film transistor (TFT), and the like arranged in a matrix thereon; a counter substrate disposed so that it is opposed to the TFT substrate and having a color filter and the like disposed in positions corresponding to the pixel electrode on the TFT substrate therebeneath; and liquid crystal interposed between the TFT substrate and the counter substrate. Liquid crystal display devices form an image by controlling the transmittance of light using liquid crystal molecules for each pixel.
Due to their flatness and light weight, liquid crystal display devices have been used in a wide variety of applications, including large display devices such as televisions, cellular phones, and digital still cameras (DSCs). On the other hand, they have a problem with the viewing angle characteristics. The viewing angle characteristics refer to a phenomenon where, when the screen is viewed obliquely, its luminance or chromaticity is changed from that when it is viewed from the front. In IPS liquid crystal display devices, which drive liquid crystal molecules using a lateral electric field, have excellent viewing angle characteristics.
Among various types of IPS is a type where a comb-shaped pixel electrode is disposed above a flat, solid counter electrode between an insulating film therebetween and where liquid crystal molecules are rotated by an electric field generated between the pixel electrode and the counter electrode. This type can increase the transmittance and is currently mainstream. Documents describing a liquid crystal display device of this type include JP-A-2007-328210. While there is also a configuration where a comb-shaped counter electrode is disposed above a flat, solid pixel electrode between an insulating film therebetween, the principle is the same.
A TFT substrate has a TFT, a video signal line, a scan line, and the like thereon and therefore has bumps and dips on its surface. For this reason, a thick organic passivation film having a thickness of about 2 μm is disposed thereon. In IPS, a counter electrode and a pixel electrode are disposed above a TFT substrate. The counter electrode is formed on an organic passivation film so that it is flat and solid, using indium tin oxide (ITO), which can serve as a transparent electrode. An interlayer insulating film is formed on the counter electrode using SiN. The pixel electrode is formed on the interlayer insulating film in the shape of a comb using ITO.
The interlayer insulating film is formed by CVD. In general, as a CVD film is formed under a higher temperature, the CVD film can adhere to the underlayer more strongly. Accordingly, a CVD film is typically formed at a high temperature of about 300° C. However, in liquid crystal display devices for which the present invention is targeted, an organic passivation film is previously formed below an interlayer insulating film, and CVD at a high temperature of 230° C. or more will change characteristics of the organic passivation film. Accordingly, the interlayer insulating film is formed by low-temperature CVD. On the other hand, formation of the interlayer insulating film by low-temperature CVD reduces the adhesiveness of the interlayer insulating film to the counter electrode formed therebeneath.
The interlayer insulating film formed by low-temperature CVD is etched to form a through hole. Subsequently, a pixel electrode is formed. After forming the pixel electrode, an alignment film is formed, baked, and then subjected to rubbing.
After the rubbing process, peeling of the interlayer insulating film from the counter electrode is often found. If the film is peeled during the rubbing process, the peeled film acts as a foreign matter, contaminating the rubbing process.
That is, disadvantageously, peeling of the interlayer insulating film from the counter electrode makes the liquid crystal panel nonconforming, as well as contaminates the rubbing process, reducing the manufacturing yield of the liquid crystal display device in the rubbing process.